THÈSE DE DOCTORAT D’AVIGNON UNIVERSITÉ École Doctorale N° 536 Agrosciences & Sciences Spécialité / Discipline de doctorat : Chimie INRAE UMR 408 « Sécurité et Qualité des Produits d'Origine Végétale » Présentée par Alexandra Bürgy MODULATION DE LA TEXTURE ET DE LA FRAGMENTATION TISSULAIRE DE FRUITS LORS DE TRAITEMENTS THERMIQUES PAR LES MODES DE CULTURE ET LA MATURATION : IMPACT SUR LA TEXTURE DES PURÉES Modulation of the texture and tissue fragmentation of fruits during thermal treatments by the methods of cultivation and maturation: impact on the texture of the purees Soutenue publiquement le 26/01/2021 devant le jury composé de : M. Marc Lahaye, Directeur de Recherche-HDR, INRAE Nantes Rapporteur M. Paul Menut, Professeur-HDR, AgroParisTech Paris Rapporteur M. Pierre Picouet, Maître de conférences-HDR, ESA Angers Examinateur Mme Catherine M.G.C. Renard, Directrice de Recherche-HDR, INRAE Nantes Directrice de thèse Mme Agnès Rolland-Sabaté, Ingénieure d’étude-Dr, INRAE Avignon Co-encadrante de thèse M. Alexandre Leca, Chargé de recherche, INRAE Avignon Co-encadrant de thèse To my parents Martina & Hans ACKNOWLEDGEMENTS Acknowledgements First of all, I would like to thank Mr. Prof. Michael Rychlik from the Technical University of Munich, who gave me the chance to live a unique experience when he proposed me an internship at INRAE in Avignon. Without him, this thesis would not exist! My sincere thanks also go to Ms. Dr. Catherine Renard, who accommodated and supervised me in the research unit UMR 408 “Securité et Qualité des Produits d’Origine Végétale” (SQPOV) at INRAE. Thank you for all the enriching meetings, your precious advices and your entire patience! I also thank my co-supervisors Agnès and Alexandre, who had always an open ear for all my questions. Thank you for your excellent guidance throughout the thesis, allowing me to develop both my personal and scientific abilities. I thank Mr. Marc Lahaye and Mr. Paul Menut for having accepted being reviewers of this thesis and Mr. Pierre Picouet for evaluating my work within the PhD jury. I would also like to thank the members of the annual PhD committee Mr. Thierry Doco, Ms. Cassandre Leverrier and Mr. Raphaël Plasson. I appreciated our discussions, which allowed me to see my work from another angle. Thank you for taking the time to follow my work! I thank the “Interfaces” project for establishing the framework, allowing me to study a fascinating research question during my thesis. I also thank Agropolis Fondation and the department TRANSFORM of INRAE for the funding of this work. Thanks to the whole unit of SQPOV, for their warm welcome and the friendly atmosphere. I especially thank the members of the team “Qualité et Procédés”: Carine and Sylvie, thank you for your scientific advices. Line, thank you for introducing me into the world of pectin analysis and your support throughout the thesis. Gisèle, thank you for the hours spent with me, the RoboQbo and the rheometer, I really appreciated it. Patrice and Romain, thank you for your technical help, either with puree processing or chemical analyses. Caro and Marielle, thank you for technical assistance. Sylvaine, thank you for being always available for all sort of questions. I would like to address a special thanks to the secretaries and computer scientists of SQPOV, Barbara, Nelly, David and Eric, who were always there to fix any problem. ACKNOWLEDGEMENTS Carla, thank you for our friendship from the first day of my arrival. I was lucky not only to share the same office but also a lot of time, good times and hard times, with you. I also thank Béa, Miarka, Alexandre do Brasil, Armand, Gaëtan and Thibault for making the time in Avignon unforgettable. During my PhD thesis, I had the chance to count with three trainees, Tanagra, Hanen and Adam, who contributed with some excellent work to this thesis. I was happy to be charged with their co-supervision, a really enriching task. I sincerely thank my family, especially my parents, for their endless love, for being always there for me and their high support. Without you, I would never have decided to go to France! I also thank Gitti, my godmother (what a nice word in English – it sums up what you are for me, a second mother), who always believed in me. And as I always save the best for the end, I thank Hervé, who supported me with his simple presence, his motivating words and his excellent cuisine. Je t'aime ! Thank you, merci & danke! Table of contents ABLE OF ONTENTS T C LIST OF FIGURES __________________________________________________ 17 LIST OF TABLES __________________________________________________ 25 LIST OF ABBREVIATIONS ___________________________________________ 29 RESUME _________________________________________________________ 35 I. INTRODUCTION __________________________________________________ 43 II. LITERATURE REVIEW ____________________________________________ 53 1. Apple fruits _____________________________________________________ 55 1.1. Basic and economic data ________________________________________ 55 1.2. Fruit composition ______________________________________________ 56 1.3. Health benefits ________________________________________________ 59 1.4. Fruit development ______________________________________________ 60 1.4.1. Impact of fruit thinning _______________________________________ 62 1.4.2. Impact of irrigation __________________________________________ 62 1.5. Parenchyma cells ______________________________________________ 62 2. Plant cell wall ___________________________________________________ 65 2.1. Generalities __________________________________________________ 65 2.2. Plant cell wall polysaccharides ____________________________________ 67 2.2.1. Cellulose _________________________________________________ 67 2.2.2. Hemicellulose ______________________________________________ 68 2.2.3. Pectins ___________________________________________________ 69 2.2.3.1. Structure ______________________________________________ 70 2.2.3.2. Pectin conformation in solution _____________________________ 77 2.2.3.3. Pectin domain linkage ____________________________________ 77 2.3. Structural organization of the plant cell wall __________________________ 81 2.4. Changes in cell wall structure during apple fruit ripening and storage ______ 82 2.4.1. Observed modifications of cell wall composition and structure ________ 82 2.4.2. Pectin degrading enzymes ____________________________________ 85 2.4.2.1. Homogalacturonan-degrading enzymes ______________________ 85 2.4.2.2. Rhamnogalacturonan I-degrading enzymes ___________________ 88 2.4.3. Other enzymes involved in fruit ripening _________________________ 90 9 TABLE OF CONTENTS 2.5. Analysis of the plant cell wall structure ______________________________ 91 2.5.1. Cell wall extraction __________________________________________ 91 2.5.2. Microstructural analysis ______________________________________ 93 2.5.2.1. Electron microscopy ______________________________________ 93 2.5.2.2. Raman imaging _________________________________________ 96 2.5.3. Nanostructural analysis ______________________________________ 97 2.5.3.1. High-performance size-exclusion chromatography (HPSEC) ______ 97 2.5.3.2. Atomic force microscopy (AFM) ____________________________ 101 2.5.3.3. Nuclear magnetic resonance (NMR) spectroscopy _____________ 103 3. Plant-based purees______________________________________________ 105 3.1. Definition of apple puree _______________________________________ 105 3.2. Physical structure _____________________________________________ 105 3.3. Apple processing into puree _____________________________________ 106 3.4. Introduction to rheology of plant-based suspensions __________________ 109 3.4.1. Rheological properties of fluids and dispersions __________________ 109 3.4.2. Methods to assess textural properties __________________________ 111 3.4.2.1. Bostwick consistometer __________________________________ 111 3.4.2.2. Stress controlled rheometer _______________________________ 111 3.4.3. Rheological properties of apple purees _________________________ 117 3.5. Determinants of apple puree´s texture _____________________________ 118 3.6. Impact of raw material and processing steps on puree´s structure _______ 123 3.6.1 Raw material ______________________________________________ 123 3.6.2. Mechanical processing ______________________________________ 124 3.6.2.1. Grinding ______________________________________________ 124 3.6.2.2. Refining ______________________________________________ 126 3.6.3. Thermal processing ________________________________________ 126 3.6.3.1. Enzymatic reactions _____________________________________ 127 3.6.3.2. Chemical reactions _____________________________________ 129 3.6.3.3. Examples _____________________________________________ 131 III. OBJECTIVES AND STRATEGY ____________________________________ 135 1. Objectives _____________________________________________________ 137 2. Strategy _______________________________________________________ 138 10 TABLE OF CONTENTS 2.1. General approach _____________________________________________ 138 2.2. Raw material ________________________________________________ 140 2.3. Process conditions ____________________________________________ 141 2.4. Combination of the results ______________________________________ 142 IV. MATERIAL AND METHODS ______________________________________ 143 1. Plant material per harvest year ____________________________________ 145 1.1. Harvest year 2016 ____________________________________________ 145 1.2. Harvest year